1. Field of the Invention
This invention relates to the field of projectile delivery systems. More specifically, the invention comprises a standoff device configured to detonate the explosives in a projectile before the nose of the projectile strikes a target.
2. Description of the Related Art
Although the present invention can be applied to many different types of projectiles, it was primarily developed as a component of existing 40 mm grenade weapons (such as the U.S. Army's M-433). FIG. 1 depicts prior art 40 mm grenade round 10. Its two main components are case 12 (which houses the propulsion system) and projectile 14. The grenade round is designed to be fired from a variety of weapons. One example is the U.S. Army's M-203 grenade launcher which is typically slung beneath the barrel of a rifle such as the M-16A2.
The launching of a 40 mm grenade involves the same principles as a conventional rifle cartridge. The main difference, however, is the size and mass of the projectile. A typical shoulder-fired military weapon launches a projectile weighing less than 30 grams at a relatively high velocity (700-1,000 meters per second). In contrast, a 40 mm grenade weapon launches a projectile weighing over 200 grams at a relatively low velocity (70-80 meters per second). Thus, while the operating principles between the two types of weapons are the same, they can be said to operate in different regimes.
The unified 40 mm grenade round 10 is placed in the launching weapon and then fired. Case 12 remains within the weapon. Projectile 14 is propelled down the weapon's bore. Rifling ring 26 engages internal rifling on the firing weapon's bore and spins the projectile in order to stabilize it in flight.
The leading end of the projectile assumes the form of ogive 28. Those skilled in the art will know that the term “ogive” sometime refers to a specific pointed shape used for missile nose cones. However, the term is also more broadly used to mean the nose portion of any flying projectile. In this disclosure, “ogive” is given the latter meaning. The ogive generally contains the arming and detonating mechanisms. The volume between the ogive and the rifling ring typically contains the explosive.
FIG. 2 shows the same 40 mm grenade round of FIG. 1 cut in half to reveal its internal details. Projectile 14 includes a hollow volume defined by the combination of ogive 28, casing 36, and aft closure 38. These three components are joined together by suitable means, such as threaded engagements.
Explosive 34 is contained within casing 36. Fuse assembly 30 is contained within ogive. It activates spitback detonator 32, which ignites the explosive. The casing is preferably scored to form a series of rectangles which will break into relatively small pieces when the explosive detonates.
The propulsion system contained within case 12 is often referred to as a “high-low” system. While a detailed discussion of this system is beyond the scope of this disclosure, a brief description may aid the reader's understanding of the environment in which the present invention operates. The “high” part of the system refers to high pressure chamber 18. This chamber is often created by the insertion of a metallic case filled with propellant into base 16. The open end of the metallic case is closed by burst diaphragm 22. A primer is contained in the opposite end.
A mechanical striker is used to detonate this primer which then causes the propellant within the high pressure chamber to ignite. This action ruptures the burst diaphragm. The expanding propellant gases are then metered through nozzle 24 into low pressure chamber 20. These relatively low pressure gases act against the aft end of aft closure 38, thereby propelling the projectile down the firing weapon's bore. For a more detailed discussion of the propulsion system of the M-433, the reader may wish to review U.S. Pat. No. 7,004,074 to Van Stratum (2006), which is hereby expressly incorporated by reference.
A detailed description of the fuse assembly is likewise beyond the scope of this disclosure. However, a fuse assembly typically contains a number of safety features designed to prevent accidental detonation. For example, in some embodiments, the fuse can only be armed when the projectile first experiences a violent forward acceleration followed by a rotation at a minimum rotational velocity. The presence of these two cues indicates that the projectile has been intentionally and successfully fired from a weapon. The fuse assembly will then arm itself during flight. Once armed, any sudden deceleration (such as the projectile impacting a surface) will ignite spitback detonator 32 and explode the grenade.
A typical fuse assembly is the M-550 fuse used by the U.S. Army. A discussion of the details of the fuse assembly is beyond the scope of this disclosure. However, the reader wishing to know these details is referred to U.S. Pat. No. 5,081,929 to Mertens (1992).
The assembly shown in FIGS. 1 and 2 functions very well. FIG. 3 shows projectile 14 flying toward a target. FIG. 4 shows the projectile striking a target and detonating. Target surface 42 is in this example a reinforced piece of concrete (a hard target). The explosion throws shrapnel 40 in all directions away from the point of impact. FIG. 5 shows the result, with void 44 being blown into target surface 42. The projectile is primarily intended as an anti-personnel weapon, and the wide dispersal of shrapnel is obviously effective in this regard.
FIG. 6 shows an idealized depiction of the detonation of explosive 34. Explosive pressure is generally emitted in a direction normal to the surface of the volume of explosive. As the explosive volume depicted is cylindrical, it will emit lateral pressure wave 50 (roughly in the shape of an expanding cylinder), forward pressure wave 46, and rearward pressure wave 48. The shape of these pressure waves determine in large part how shrapnel created by the explosion will fly.
It has long been known to use a 40 mm grenade as a door breaching round. However, it is often not optimal in this role. In anti-insurgency operations, soldiers must often penetrate occupied buildings. In many instances, it is not known whether the occupants are hostile. However—hostile or not—the occupants will not voluntarily open the door. Thus, the door mush be breached.
FIGS. 7 and 8 shows the use of a prior art 40 mm grenade round in this role. In FIG. 7, projectile 14 impacts door 52 at a significant velocity (typically about 70 meters per second). Ogive 28 knocks breach 54 into the face of the door. The sudden deceleration ignites the fuse assembly, so spitback detonator 32 ignites the explosive. FIG. 8 shows the result. The expanding pressure waves from the exploding projectile destroy the door and explosion 58 sends flying debris 56 into the occupied structure. Persons within the structure may be injured or killed.
Thus, while the prior art 40 mm grenade round is effective in breaching doors, it may produce unwanted collateral damage. A system which can breach the door without throwing shrapnel into an occupied structure would be preferable.